In recent years, electronic devices having a semiconductor layer, such as a thin-film transistor (TFT), a photo sensor and a light-emitting element, have been used in various products. Specific products using such an electronic device are, for example, active matrix drive display devices such as liquid crystal display devices and organic electroluminescence (EL) display devices. In an active matrix drive display device, TFTs are used as the electronic devices.
In display device products, TFTs in which a silicon layer is used as a semiconductor layer are commonly used. In recent years, however, more attention has been paid to coating-type TFTs in which an organic material layer is used as a semiconductor layer. Unlike silicon crystals bonded by atomic bonding, organic materials are bonded by intermolecular forces, and hence organic materials are flexible. Therefore, by using TFTs in which an organic material layer is used as a semiconductor layer, it is possible to realize lighter and thinner electronic devices compared to electronic devices using TFTs in which a silicon layer is used as a semiconductor layer. Such a configuration also provides flexibility to the electronic devices. For this reason, there is a proposal to use such coating-type TFTs in next-generation display devices, electronic paper, and so on.
As examples of coating-type TFTs, bottom gate type organic TFTs are known. FIG. 14 is a cross-sectional view illustrating a configuration of a conventional TFT 900. As shown in FIG. 14, the conventional TFT 900 includes a substrate 901 and the following components sequentially formed on the substrate 901: a gate electrode 902; a gate insulation layer 903; a source electrode 904S and a drain electrode 904D as a pair of electrodes; a bank 905A having an aperture 905B located above the gate electrode 902; and a semiconductor layer 907 located within the aperture 905B of the bank 905A. Furthermore, a protective film 908 is formed on the semiconductor layer 907.
Patent Literature 1 discloses forming a semiconductor layer by a coating method.